Hitherto, there has been known a fin-and-tube heat exchanger including a plurality of plate-shaped fins, which are arranged at predetermined fin pitch intervals and extend in the gravity direction, and a plurality of heat transfer tubes (hereinafter referred to as “flat tubes”), which each have a flat cross-sectional shape. Each flat tube is joined to the fins, for example, by brazing, and extends in a horizontal direction so as to cross the fins. An end portion of each flat tube is connected to, for example, a distributor or a header which forms a refrigerant flow passage together with the flat tubes. In the heat exchanger, heat is exchanged between heat exchange fluid such as air which flows through the fins and heat-exchanged fluid such as water or refrigerant which flows in the flat tubes.
In a heat exchanger using flat tubes as heat transfer tubes, as compared to a heat exchanger using circular tubes, a larger heat transfer area can be secured in a tube, and flow resistance of the heat exchange fluid can be suppressed, thereby enabling improvement in heat transfer performance. Meanwhile, with regard to drainage performance of the heat exchanger, the cross-sectional shape of the flat tube is liable to cause water droplets to remain on a tube surface of the flat tube, and hence drainage performance of the flat tube tends to be lower than that of the circular tube.
For example, during a heating operation of an air conditioner, moisture contained in air being the heat exchange fluid is condensed to adhere to a heat exchanger of an outdoor unit, with the result that frost is formed. In general, a defrosting mode is provided for the purpose of preventing increase in flow resistance and degradation in heat transfer performance as well as damage to the heat exchanger due to frost formation. However, when water droplets remain, the water droplets are frozen again and grow into larger frost. Thus, when the drainage performance is low, it is required to extend a time period of an operation in the defrosting mode. As a result, degradation in comfortability or degradation in average heating performance may occur.
In view of the above-mentioned circumstances, in Patent Literature 1, there is disclosed a heat exchanger in which flat tubes are inclined in the gravity direction for the purpose of improving the drainage performance (see Patent Literature 1).